Chomsky hierarchy

The Chomsky hierarchy is a concept of theoretical computer science. Noam Chomsky looked at grammars of regulär language and classified them into four Levels, numbered 0 to 3. Group 0 consists of the regulär exressions without rstriction, groups 1 to 3 contain restrictions. A grammar with a bigger number must also satisfy the constrains of all the grammars with Power numbers. The concept was Developer in the 1950s.